JPH0240515Y2 - - Google Patents

Description

[Detailed description of the invention] <Technical field of the invention> This invention is a method for sequentially inspecting products or parts that must not leak fluid during use or must meet a certain standard during the production process. However, regarding leak testing equipment that determines pass/fail, it has a learning function that can automatically correct errors in measurement data caused by the measurement atmosphere, etc., and also has a self-check function of the testing equipment itself. It is an object of the present invention to provide a differential pressure detection type leak testing device having the following features.

<Background of the invention> Confirming the airtightness of various products that require airtightness, such as containers for storing liquids, hydraulic circuits for automobile brake systems, radiators, and even gas products. is required.

There are two ways to test the airtightness of these various products: applying a constant air or vacuum pressure to the product, measuring changes in air or vacuum pressure with a pressure gauge, and testing for leaks. There is a method in which a leak-free comparison tank is provided for the test object, and the pressure difference between the comparison tank and the test object is measured to check for leaks in the test object.

The former testing method has the disadvantage that it is difficult to detect minute leaks because it is necessary to detect minute changes in the pressure value while a constant pressure is applied.

On the other hand, the latter method tests for leaks by measuring the pressure difference between the comparison tank and the object to be inspected, so it is possible to greatly amplify the electrical output of the differential pressure detector. As a result, it has the feature of being able to detect even minute leaks. Therefore, differential pressure detection type leak testing devices are mainly used.

<Description of Prior Art> FIG. 1 is a block diagram showing the configuration of a leakage testing device that has already been put into practical use. A flow pipe 10 connected to the output side of the air source 11 is divided into two parts at the outlet side of the solenoid valve 14 via a pressure regulating valve 12 and a solenoid valve 14, and is connected to branch passages 15-1 and 15-2, respectively. A pressure gauge 13 is connected between the outlet of the pressure regulating valve 12 and the inlet of the electromagnetic valve 14 for setting the test pressure.

The branch 15-1 connects to the conduit 18 via the solenoid valve 16.
The conduit 18 is connected to one end thereof, and the other end of the conduit 18 is provided with a mechanism for connecting an object 20 to be inspected for leakage. A mechanism at the other end of the conduit 18 connects the objects 20 to be inspected one after another to enable leakage inspection. On the other hand, the branch path 15-2 is the solenoid valve 1
7 to one end of a conduit 19, and the other end of this conduit 19 is connected to a reference tank 21. Conduit 1 on the outlet side of solenoid valves 16 and 17
A differential pressure detector 22 is installed between 8 and 19.

The output signal of the differential pressure detector 22 is given to a comparator 32 via an amplifier 31, and the comparator 32 is configured to be able to compare it with the output reference value of the reference signal setter 33.

<Explanation of operation in Figure 1> The object to be inspected 20 is attached to the end of the conduit 18, the leak-free reference tank 21 is attached to the conduit 19, the solenoid valve 14 is closed, and the pressure regulating valve 12 is opened to read the pressure gauge. 13 adjusts the air pressure provided from the air source 11 to a predetermined value. Next, solenoid valve 1
6 and 17 are opened, and the solenoid valve 14 is opened to send air at a constant pressure to the branch paths 15-1,
15-2, and are supplied to the test object 20 and reference tank 21 through conduits 18 and 19, respectively. This state is defined as a pressurization or exhaust period as shown in FIG. 2A, and the time period is represented by _T1 .

A certain period of time after opening the solenoid valves 16 and 17
After T ₁ has elapsed, the inspected object 20 and the reference tank 21
After the internal pressure stabilizes, the solenoid valves 16 and 7 are closed. Furthermore, a predetermined stabilization time T ² (this time T ₂
(referred to as stabilization time), the zero correction signal 34 is sent to the automatic zero correction amplifier 31 connected to the differential pressure detector 22.
is given, the output of the amplifier 31 is set to zero in advance, and a certain period of time is set from this zero setting point.
After T ₃ the output signal of amplifier 31 is read. Time from zero setting to reading T ₃
It is called the inspection period. When the zero point of the amplifier 31 is set, the sensitivity of the amplifier 31 is switched to a high sensitivity state. Therefore, when the output of the amplifier 31 is read, the detection signal of the differential pressure detector 22 is greatly enlarged and read.

Here, there is a period T ₁ in which the solenoid valves 16 and 17 are controlled to open and pressure is applied, a period T ₂ in which the solenoid valves 16 and 17 are closed to stabilize the pressure, and a period from when the amplifier 31 is set to zero until reading is performed. The entire inspection period _T3 is referred to as one inspection cycle. Switching between the periods T ₁ , T ₂ , and T ₃ is performed by the sequence controller 49.

When the inspection object 20 is completely airtight and there is no leakage, the output signal from the amplifier 31 ideally becomes zero during a certain detection time. When there is a leak in the inspected object 20, an output signal is obtained in which the positive pressure gradually decreases if the internal pressure is positive, and the pressure gradually increases if the internal pressure is negative, and the output within a certain detection time The signal has a value that is approximately proportional to the amount of negative or positive leakage.

The reference signal given from the reference signal setter 33 and the output signal of the amplifier 31 are compared by the comparator 32,
A quality determination output 35 indicating whether the product is good or defective is obtained depending on whether the output signal does not exceed the reference signal.

<Problems with the conventional differential pressure detection type leak testing device> In this conventional differential pressure detection type leak testing device, even if the reference tank 21 is exactly the same shape as the test object 20 and has no leakage, Inspection object 20
The output signal cannot ideally be zero because it is affected by factors such as the temperature, internal capacity, slight deformation of shape, and difference in adhering moisture between the tank 21 and the reference tank 21. In other words, due to these factors, even if there is no leakage in the test object 20, the output signal within a certain detection time will not be in the ideal zero state, and will have a certain positive or negative state as shown in FIG. 2B. It usually shows a value ΔP comparable to the amount of leakage.

If the errors caused by these factors are always constant for each measurement cycle, they can be corrected in advance during use, but in reality, the errors caused by long-term atmospheric conditions, such as ambient temperature, humidity, supply air temperature, and Factors such as the temperature of the test object 20 and the reference tank 21, and the attached moisture gradually change.

In addition, deformation of the rubber that seals the opening of the inspection object 20 may occur, and based on these factors, when testing for leaks one after another on a large number of inspection objects 20 flowing through a production process line, it always takes more than one day. Errors based on these factors change from time to time, from day to day, or from season to year.

<Disadvantages of the conventional differential pressure detection type leak test device> In the conventional differential pressure detection type leak test device, there is an error based on factors that change with time, and the output reference value of the reference signal setting device 33 for pass/fail determination exists. I had to change it frequently. This is not desirable in a leak testing device intended for labor saving and automation, and it has been difficult to perform highly accurate leak testing due to this operation.

In addition, in order to accurately measure the amount of leakage, it is better to take longer pressurization and stabilization times T ₁ and T ₂ , but if the pressurization and stabilization times T ₁ and T ₂ are longer, the inspection time for one product will increase. It also has the disadvantage of being less efficient.

Furthermore, if a leak occurs in the air passage itself during the inspection, even if the object to be inspected is non-defective, it will simply be determined that the object to be inspected is defective. Therefore, the conventional leakage testing device has the disadvantage that it cannot detect defects in the testing device itself.

<Purpose of the invention> This invention can shorten the inspection time for each inspected object, has the function of automatically correcting errors based on factors that change over time, and also has the function of automatically correcting errors based on factors that change over time. It is an object of the present invention to provide a leakage testing device that can detect failures using a self-check function.

<Summary of the invention> In this invention, an error value is obtained for each measurement cycle, and this error value is averaged and used as a correction value for each measurement data, thereby automatically correcting changes in various factors. In order to be able to perform high-precision leak testing, we also prepare other reference products for the test object, use this reference product to determine the initial error of the inspection device, and start operation based on this initial error. It is configured as follows. In addition, by adding correction values to each measurement data and correcting it, the inspection time can be shortened, and many objects can be inspected in a short period of time. Each time the number of cycles elapses, the pressurization and stabilization time is set longer, and the measurement value obtained after this long pressurization and stabilization time is used to check whether the correction value used for each measurement cycle is correct or not, and to check. It is constructed so that it can self-check the quality of the device itself, that is, the quality of the air circuit.

<Example of the invention> Fig. 3 shows an example of the invention. In FIG. 3, parts corresponding to those in FIG. 1 are designated by the same reference numerals. The difference from FIG. 1 is that a branch path is connected to the flow pipe 18 side, and a third solenoid valve 3 is connected to one branch path 18-1.
6 is connected, and through this third solenoid valve 36, a reference product 37 among the objects to be inspected 20 that has been determined to be non-defective is connected.

A fourth solenoid valve 38 is connected to the other branch pipe 18-2, and the object to be inspected 20 is connected through this fourth solenoid valve 38. Here, the solenoid valve 17 will be referred to as a first solenoid valve, and the solenoid valve 16 will be referred to as a second solenoid valve.

An A/D converter 39 is provided on the output side of the amplifier 31 to perform A/D conversion of the differential pressure detection value of the differential pressure detector 22 output from the amplifier 31, that is, the measured value. The measurement data digitally encoded by this A-D conversion is sent to the correction value correction means 40 and the data correction means 4.
4. The correction value automatic correction means 40 is constituted by a data storage device 41 and an average value calculation device 43. A data upper limit discriminator 42 is attached to the storage device 41 . This data upper limit value discriminator 42
is operated so as not to store in the storage device 41 those output differential pressure values exceeding a certain limit value among the differential pressure values obtained from the differential pressure detector 22. The upper limit value for determining whether to memorize or not is set as the fourth
Let ΔP _M be as shown in the figure. Therefore, measurement data exceeding the upper limit value _ΔPM is not taken into the storage device 41.

The number of data that can be stored in the storage device 41 is limited to N, for example, and when N or more data are read, the oldest data is pushed out. Therefore, the latest N pieces of data are always stored in the storage device 41.

An average value calculation circuit 4 is provided on the readout output side of the storage device 41.
3 will be provided. This average value calculation circuit 43 calculates the average value of the N pieces of measurement data stored in the storage device 41, and supplies the average value to the data correction means 44 as a correction value.

By configuring the correction value automatic correction means 40 in this way, the average value output from the average value calculation circuit 43 is always obtained based on the latest N pieces of measurement data. Even if the value gradually changes due to changes in the factors, it is possible to obtain a correction value that follows the change.

In the data correction means 44, each measurement data outputted from the A-D converter 39 is added to the correction value automatic correction means 4.
The correction value output from 0 is added to correct the measurement data. The result of this correction is shown in FIG. 4B. In other words, by subtracting the correction value from _the inspection data D ₁ , D ₂ .

The corrected data corrected by the data correction means 44 is transmitted to the leak amount display 45 and the quality judgment means 46.
supplied to The pass/fail judgment means 46 is provided with pass/fail limit value setting means 47 that determines the limit of pass/fail, and the corrected data is set to the limit value ΔP _S in the setting means 47.
If the corrected data is within the range of △PS, a good signal 48 is output, and if the corrected data is outside the range of the limit value △P _S , a bad signal 4 is output.
8' is output.

Reference numeral 49 indicates a controller that sequentially controls the overall operation. This controller 49 controls the operation of each part.

<Description of operation of the device> At the start of operation, the first, second, and third solenoid valves 17,
16 and 36 are opened, and air pressure is applied to the comparison tank 21 and the reference product 37 determined to be good. When a predetermined air pressure is applied to the comparison tank 21 and the reference product 37, the first and second solenoid valves 17 and 16 are controlled to close, and when a predetermined equilibrium time _T2 has elapsed, a zero setting signal 34 is sent to the amplifier 31. is given, and the output of amplifier 31 is forcibly set to zero. Along with this, amplifier 3
Switch the gain of 1 to a large state.

When the predetermined measurement time _T3 has elapsed since the output of the amplifier 31 was set to zero, the A-D converter 3
9 is taken into the storage device 41 as an A-D conversion output.
Here, if this measured data value is larger than the error upper limit value ΔP _M , the storage operation is blocked and no storage is performed.

However, in this initial operation, the comparison tank 21
Since the reference product 37 is connected to the reference product 37, the differential pressure value therebetween is small. This small differential pressure value is an error based on various factors. Therefore, the first measurement data is taken into the storage device 41 as a correction value, and at the same time, the data is read out and the average value calculation means 43 outputs the average value. Since this average value has one data item, the measured data value is output as is as a correction value.

The data correction means 44 subtracts the correction value from the measurement data output from the A-D converter 39 to obtain corrected data. Since the initial measurement data and the correction value are the same value, the corrected data is zero.

When the initial correction value is held in the average value calculation means 43 by the first measurement, the third solenoid valve 36 is closed, and the fourth solenoid valve 38 is controlled to be open in its place.
In this state, the inspection of the inspection object 20 is started.

In this invention, in particular, every time a predetermined inspection cycle is completed or every time a certain period of time
As shown in the time point T ₀ in the figure, the pressurization and stabilization time is the pressurization and stabilization time T ₁ of the other inspection cycles,
The operation of inspecting the object 20 to be inspected is performed by changing the pressurization and stabilization times T ₁ ′ and T ₂ ′ to be longer than T ₂ . If the differential pressure changes rapidly at the start of this operation, that product is defective, so that product is removed and a product that is close to good is used.

In other words, the incidence of defective products on the production line is extremely low, and most products can be considered good.
Therefore, even if you select a product that happens to be connected, it can be considered to be a good product in most cases. Therefore, it is essential to select the pressurization and stabilization times T ₁ and T ₂ to be longer than normal times T ₁ ′ and T ₂ ′ every time a predetermined measurement cycle is completed or a predetermined time elapses. The measurement error becomes smaller, and the measurement data obtained at that time can be supplied to the pass/fail judgment means 46 without correction, and the pass/fail judgment can be made without correcting the measurement data.

In addition, an error upper limit value △P _M is set, and the measurement data exceeding this value is not taken into the automatic correction value correction means 40, so that the measurement data when a leak occurs in the air pressure supply path etc. will be changed to the correction value. It is possible to avoid an excessive increase in the correction value.

<Effects of the invention> According to this invention, each time each inspected object 37 is inspected, the measurement data is taken into the storage device 41, old measurement data is removed, new measurement data is added, and the average value is calculated. Since the average value is used as the correction value, even if the error value fluctuates due to various factors, the correction value will be corrected to follow the fluctuation, so you can always perform highly accurate leak inspections. .

Furthermore, since a correction value is added to the inspection data, if the object to be inspected is a good product, the corrected data will be close to zero. Therefore, the pass/fail judgment limit value in the pass/fail judgment means 46 can be set to a small value.
Therefore, highly accurate pass/fail judgments can be made. In addition, since the judgment limit value can be set to a small value, even if the pressurization and stabilization times T ₁ and T ₂ are short, the inspection data of the inspected object with minute leakage will reach the judgment limit value early. , it is possible to reliably discover defective products. Therefore, the time for each inspection cycle can be shortened, and a large amount of inspection can be performed in a short period of time.

Furthermore, in this invention, the pressurization and stabilization time is extended longer every time a predetermined number of inspection cycles or a predetermined time is reached, and by extending this time, the self-check of the air flow passage and whether the correction value is correct or not. Since it is determined whether or not the inspection device itself is tested, it is possible to perform a self-diagnosis of the inspection device itself. Therefore, a highly reliable leak test can be performed.

In other words, by selecting long pressurization and stabilization times T ₁ and T ₂ , it is possible to sufficiently detect a leak when it occurs in a sealed jig piping or the like other than the object to be measured 20 . This operation prevents excessive error correction due to continuous leakage from objects other than the above-mentioned object to be inspected in the normal short pressurization and inspection cycle with stabilization times T ₁ and T ₂ .

In the above, an example has been explained in which each block is configured such as the correction value automatic correction means 40, the data correction means 44, the pass/fail judgment means 39, the controller 49, etc., but if these are configured by a microcomputer, it can be made with a simple structure. be able to. As a result, it can be manufactured at low cost.

[Brief explanation of the drawing]

Fig. 1 is a block diagram to explain a conventional differential pressure detection type leak test device, Fig. 2 is a waveform diagram to explain the operation of the device shown in Fig. 1, and Fig. 3 is a waveform diagram to explain the operation of the device shown in Fig. 1. A block diagram showing one embodiment, FIG. 4 is a graph for explaining the operation of this invention, and FIG.
The figure is a waveform diagram for explaining the operation of this invention. 11: Air pressure source, 17, 16: First and second
Valve, 20: Test object, 21: Comparison tank, 22:
Differential pressure detector, 36, 38: third and fourth valve, 3
7: Standard quality adjustment, 39: A-D converter, 40: Correction value automatic correction means, 41: Storage means, 43: Average value calculation device, 44: Data correction means, 46: Quality determining means.

Claims (1)

[Claims for Utility Model Registration] A. An air pressure source that generates a predetermined positive or negative air pressure, and B. The air pressure generated in this air pressure source is the first air pressure.
the air pressure generated in the comparison tank provided through the valve and the air pressure source C in the second
a reference product provided through the valve and the third valve; D a product to be inspected to which the air pressure generated in the air pressure source is provided through the second valve and the fourth valve; E the pressure in the comparison tank and the reference product. A differential pressure detector that detects the pressure or the difference between the pressure in the comparison tank and the pressure in the product to be inspected; an initial correction means for measuring the pressure difference between the two and obtaining an initial correction value based on the measurement result; A correction value correction means for measuring differential pressure and obtaining a correction value from the average value of the measurement data; H. A gate means for preventing measurement data exceeding a predetermined value from being provided to the correction value automatic correction means; I: a data correction means for measuring the differential pressure between the comparison tank and the product to be inspected, and correcting the measured data with a correction value obtained from the correction value automatic correction means; and J: correction obtained from the data correction means. a pass/fail determining means for determining whether the inspected data is within a pass/fail determination limit and outputting a pass/fail signal; With the non-defective product connected, set the pressure in the comparison tank above and the pressurization and stabilization time for the non-defective test object to be longer than the time for other test objects, and then calculate the pressure based on the measurement results. A differential pressure detection type leak testing device having a learning function, comprising: means for determining whether or not the correction value outputted by the automatic correction value correction means is correct and whether or not the air pressure supply path is good or bad;